Since the late 1970s, diesel particulate filters (DPF) have been studied as an apparatus for filtering particulates of exhaust gases in diesel engines. However, to develop engine designs and improve fuels could meet the environmental regulation standards by the 1980s, without equipping DPF. DPF has been actively studied after 1980 to meet stricter regulation standards. Said DPF should remove particulates included in exhaust gases by trapping them. Also, said DPF should have the performance that burns particulates before affecting engines by the resulting pressure drop and fully removes them, besides thermal resistance and durability. Such DPF may be classified into the following groups: honeycomb monolith filters, ceramic fiber filters, and metal filters. Among these, said honeycomb monolith filters have disadvantage of very little resistance to heat impact at high temperature and low durability, and said metal filters have disadvantage of low thermal resistance and low resistance to corrosion despite low cost and easiness for production. Therefore, study is recently carried out about fiber filters using ceramic fibers. Such ceramic fiber filters are prepared in the forms of foam, extrusion, and non-woven paper. Foam and extrusion forms have low resistance to heat impact and extruded honeycomb forms have disadvantage of low gas permeability due to low porosity rate, whereas non-woven paper forms are known to have high porosity rate and high removal efficiency of particulates.
Therefore, it needs to prepare novel ceramic filters having excellent gas permeability due to high porosity rate as well as strong resistance to heat impact in form of non-woven paper.